Relayless line circuit



March 25, 1958 A. HEMEL RELAYLESS LINE CIRCUIT Filed April 17, 1956phone and Telegraph Corporation, New York, -Ns-Yr,

a corporationof'Marylandv f Application April 17,1956, serialNo. s78582311 claims.v (ci. 179-18) This invention relates in general to relaylessline circuits suitable for use with two-wire -lines used in lswitchingsystems. Its principal object is to provide a satisfac tory and reliablerelayless line circuits of' theindicated type which provides the generaloperational featuresuof a line circuit having both aline relay and acutoi relay;

In prior -attempts of this nature; the individual .line relays werereplaced by arelatively small number. of line relays common toall thelines -of a group and-each individual cutol relay was replaced'v byanumber offresistances 'of high value. In such-attempts-, thecommon linerelay arrangement was unsatisfactory asfitsluse; was limited to smallprivate switchboards serving 'well-insulated lines located largelyinside of buildings as'theicumui lative line leakage, particularlytoground, oftenfresulted in false operationof the line relay. Thefuse of.resistance networks in place of cutoi -relays was likewiseunsatisfactory as parasitic'current ow throughsuch resistances oftenestablished a` potential on'the testrconducto'r which resultedinfalsender operation. Also, such resistances often reduced the etfect-iveringingvoltage duringthering'- ing period.Y f

According .-to the invention,- af common line frelay? ar,- rangement isemployed which isenot subject to talsevop.- eration fromleakage toground and animpedancenet'- work arrangement is employed inplacev ofVthe usual ,eutoff relay which does not permit current flow from thefline conductors throughthe network other thandu'ring line-A finding`action.

The disclosed arrangement isA suchthat one"o`f line con"- ductors isconnected to a negative pole or tap of theexchange battery through acommon line relay infse'ries with a rectifier diode; the otherconductorV of the-linefis connected to a more negative pole or tap ofthe exchange battery over a-series circuit path through a rectifierdiode and a resistor; and the test or sleeve conductor Aiscconnected tothe midpoint of the rectifier and resistor.' g In such an arrangement,inresponse-to initiation of a call, current flow through the line relayandpassociatedrectier diode circuit, over the line loop, and through-theseries diode and resistor` circuit operatesthe line relay to control theextension of a tin'der connection, the rectiier diodes being poled topermit current tiow from the iirst battery tapto the more negativebattery tap. After linending action, or seizure of a'called lineterminal, the sleeve conductor becomes closed an grounds the junctionpoint of the rectiiiery diode and `series resistor. .This ground masksthe vhi-gh negative potential and, depending A United States; Patent"JAon the polarity of the usual' battery' feed Vconnection vto ductorl ofiaV ca'lledline;l I

by the `normalI ringing Avoltageapplied 'to the line ron-v 2,828,365Patented Mar, 25.,

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Thepabove-mentioned andyother features and objects of thisinventionandlthe manner of attainingfthern will becomejmore apparent and'- theinventionzits'elf-will'be Abest-understood,l by reference to' the`followingfdescription of an -embodiment of -theinvention takenv .inconjunction withfthe acconlpanyingdrawin'g` whereina group o'f relaylessline equipments -and'associated switching and rcontrol stages areshownfor extending ing and cal.led-1ines.V p Y For brevity,v thedisclosed-system serv'es'ltlOl lines `-of which only lines L1 `and L10of the rs't Vten-line group are shown.- A' common'line relay; suchas'iCL-I, is providedfor each group of ten lines, the'commonline relaybeing associated with rthe lines ofy its group overextension-conductors-such as .ET-1 to' ET-10 and associated isolating.rectiers; suchfas and 116.v` VThe usual individual cutoff relaysare-each replaced byfan impedance networkl comprising a rectifierdiode,` such vas 111,- and anassociatedresistor 112.

p The common line relay of eachten-line group is -associatedY with.controller-CR-l .overV associated control Vconductors such as TM-l, 1-Aand 1B and the individual lines of'v-such-group are;associated with thecontroller over -respectiveunits .mark conductors UM-l 'to UM'-1tl.

Controller IGR-f1 is generally similar to the' controller disclosed inzthe?U.S:patent application of EJ; Leonard, for aACrossbar-Switch'iLine-Finder System, Serial'y No. 468,443;V tiledNovember Vl2, 1954;` now Patent No. 2,768,240,- suclI-controller beingarranged to .respondio a ground tens and units-mark. The unitsmarkfro'n'i the relayless-linevcircuit, is :different from'tlie'unitsmark of thenoted Leonard application, butthe operation 'ofVthefcontroller is generally similar,. as'willappear hereinater.- f I' Adetailed description .ofgthe invention Awill "now vbe given l bydescribing. the operationsl involved in extending a-connection'irom `acalling line, such' as'- line L=1-,.tofa`n idle originating trunk'OTlextendingito ain-idle` connector. Avk further description will then dealwithl thefoperation of the vconnectorr in 'further vextending fthefconn'ectio'n' to a called line L101and in'applyingringingcurrenttlereon to signal' thecalled party.

Y In response to the removal ofthe receiver (not-shown) by thesubscriber at station S1 on line'Ll; the usuallline loop Iis-closedacross thettip and ring conductorsTandRg closing ain-operate circuit forthe'associatedcomnonlin relay.GL-1. This circuity is` from a`negative'tStilvoltfpo tential to a' 'negative -75-voltpotential through'tlewin'd4 arrangement is provided, as will hereinafter be describ'dg"which'l individualizes the controllerwitlrionlyonecom:

.mon linerelay at any oneV time.

The'y ground on the tens mark conductor: TM`1` i'sfex'- tended' throughrectifier 26S'and 'through break contacts 2 oftstart'relaylz to thebatterylconn'ected"winding'of preference-'shift' relay i213.A u Y,

' Preferencefshift'relay 213' operates and at'iltfslrnaker"COri` factsE1l an'dZ' 'advances each of the :switches 2411' and 242 connectionsbetween cll- 3 one step and at itsV contacts 3 closes an operate circuitfor start relay 212.

Start relay 212 operates from ground on therelease wire RLSE and locksthereto through its make contacts 5. Make contacts 1 of relay 212'closean operate circuit forY time relay 214 which operates and times theinterval that controller CR-l may be held for use on any one call; itsbreak contacts 2 open the operate circuit of relay 213; its makecontacts 4 extend ground potential to lock wire L; its make contacts 6cause the tens switch 241 to progressively advance its brushes'acrossits associated contact bank in search for thel calling ten-line group oflines; and its make contacts 3 connect the batteryconnected winding ofthe tens-test relay-211 to the brush of tens switch 241 in preparationfor detecting the calling ten-line group in response to the brush ofswitch 241 engagingthe grounded tens-mark conductor TM-1.

Assuming the one pulse generated by preference shift relay 213 to haveadvanced the brushes of switch 241 to position 1, the battery potentialappearing on the brush of switch 241 from the battery-connected windingof relay 211 is extended through the winding of tens-group relay 201 tothe ground appearing on the tens mark conductor TM-l, operating thetens-group relay 201 and the tenstest relay 211 in series.

Responsive to the operation of the tens-group relay 201, batterypotential from current-limiting resistor 112, through rectifier 111,over the calling line loop, over conductor ET-L through make contact lof relay 201, and ,through break contacts 1 of relay 216 appears on thebrush of units switch 242, which responsive to the noted operation ofrelay 211, advances its brush across its contact bank under control ofinterrupter P240. At the sameV time, relay 201 locks operated at itscontacts 11 and at its break contacts 12 restores common line relayCI.-1.

Responsive to the engagement of the brush of the units switch 242 withthe switch bank contacts associated with units mark wire UM-l, runitstest relay 215 operates from current ow resulting from thev-voltdifference potential appearing on wire UM-l and locks to the ground onlock Wire L. At the time that switch 242 was advancing, the extensionconductor ET-l was free from all unnecessary current consuming sourcesas relay CL-l was opencircuited by the operation of relay 201.

As described in the noted Leonard application, controller CR-1, inresponse to the operation of relay 215, functions to cause fmder switchFS to extend a connection from the calling line L1 to an idleoriginating trunk OT1 extending to the next switching stage. Responsiveto seizure of the next stage, ground is returned on sleeve conductor Swhich is connected to the midpoint of rectierlll and resistor 112.` Atsuch time, controller CR-1 is cleared out and returned to normal'use inpreparation for another call. l.

Upon completion of the described line-nding action and the consequentseizure of connector CONN-1, the batteryand ground-connected windings ofthe batteryfeed line relay of the connector are connected to the tip andring conductors of the calling linesover originating trunk OT1 andthrough tinder switch FS. Also, ground potential is present on thesleeve conductor of the relayless line circuit. Y

Responsive to the appearance of ground at the midpoint of rectier 111and resistor 112, all current flow from the tip and ring conductors Aofthe calling line through any elements of the relayless line circuitceases as the ground potential on the sleeve conductor masks the Ynegative 75-volt potential. The operation is as follows:

Assuming that connector ACONN-1 was seized with re-A versing relay REVrestored, then ground potential from the upper winding of the line relayof the connector ap-f pears on the tip conductor T of the line circuitand negative 50 volts from the lower winding of the line relayappears onthe ring conductor Rot the line circuit.- i

With ground from the tip conductor appearing on one side of rectitier115 and negative 50-volt battery potential appearing on the other side,no current ows through rectifier 115 as it is poled ,to permit currentow only when the tip conductork is more negativerthan the line relaywinding battery supply, such condition only being vpresent duringline-finding action when the negative 75 Volts is not masked by groundon the sleeve conductor.

The appearance of negative -volt potential on the ring conductor doesnot permit current ow through rectilier 111 to the grounded sleeveconductor as rectitier 1.11 isrpoled to permit current flow only whenlthe ring c'z'oncluctor is more positive than-the potential appearing onresistor 112, such condition also only arising during line-findingaction.

Assuming that the reverse relayV in connector CONN-1 operated toprovide'supervisory functions, then a negative 50-volt potential appearsVon the tip conductor T and ground potential appears on theringconductor R. Under such conditions, rectifier 115 has a negative 50-voltpotential on both sides and rectie'r 111 has ground potential on bothsides and consequently no current flows from either line conductorthrough the line circuit impedance elements. Y

In addition to the disclosed arrangement preventing any parasiticcurrent flow through the -line Ycircuit elements from the lineconductors after line-finding action, the common line relay arrangementis such that its operation is positive and reliable as regards lineleakage. The common line relay does not operate from the cumulative lineleakage to ground of a number of lines effectively in parallel asrectifier 115 is poled to permit current tlow from the line conductorsonly when they are more negative than the negative 50-volt potential ofthe winding ofl the line relay. Further, the common line relay isarranged to be reliably restored upon completion of lineflnding actionirrespective of the low bridging resistance of a number of lines as itsoperate circuit is openby the controller, as previously noted.

In addition to ythe foregoing, therectiers, such as 115 and 116,isolatereach line from the others so that fault conditions on one of thelines will not disable the others.

From the foregoing, it can be seen that current flows through therelayle'ss linefcircuit impedance elements only during call-initiationVto thus operate the common line v relay. tall other'times, parasiticcurrent ow therethrough Vis prevented. 5

The following portionof the description relates to the operation oftheconnector in extending the desired connection to a'callerd lineV and insignalling the subscriber thereat.V ,n Y' l, Y

Responsive tothe dialing V.of the directory number of the `calledAsubscriber, operations' Voccur in connector CONN-1 and itsassociatedcontroller (not shown) to operate the connector. switches CS to extendthe connection tothe calledV line in thewell-known manner.

. When connector switch CS operates to extend a connection to line L10,IVground isjprojected'forward on the permitY currentflow only whenthering conductor becomes more positive than Vground or the tipconductorbecomes more negative Vthan ground, and unless compensated forthe amplitude of the usual ringing voltage which normally exceeds 5()volts in both the positive and negative directions, would permit theline conductors to assume potentials which would permit rectitiers 111and 116 to conduct. The consequent current drain would therebyeffectively reduce the ringing voltage. To prevent conduction of therectiiier during ringing voltage application, one of the generatorsupply leads is connected to a negative l5() volt potential throughresistor mi), and the other lead is connected to ground. ln this way,the tip conductor is maintained at a ground potential so that no currenttlows through rectifier M6 during ringing and the ring conductor ismaintained negative with respect to ground from the negative 150 voltsuperimposed ringing voltage so that no current flows through rectier113. Thus, the positive and negative half cycles of the ringing voltagedo not overcome the sleeve masking arrangement.

Responsive to called line answer, the ringing generator is disconnectedfrom the line conductors and the usual backbridge relay or calledbattery-feed supply relay is connected to the line conductors, thepotentials on the called line conductors then being the same aspreviously described with reference to seizure of the connector, andcurrent ilow through the rectiflers is prevented.

From the foregoing, it can be seen that during called party signallingand after called party answer thereby, parasitic current flow fromeither line conductor through the impedance network is also completelyrestricted.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention.

I claim:

j 1. In a communication system, a switchboard terminating a group ofnormally open lines any one of which becomes closed when calling, adirect-current source common to the lines and connected to each line tosupply signalling current flow thereover in a given direction whencalling, the connection from the current source to any line including anindividual path which includes a resistive element adjacent to one poleof the current source and a serially related uni-directional diodeadjacent to the line, call-detecting means including means for detectingsignalling current iiow over any line, vmeans for answering a detectedcall on any line, and means included in the call-answering means formaking a connection at the junction of the said resistive element andthe said diode thereof which terminates the said flow of signallingcurrent thereover by masking the potential normally applied through theresistive element.

2. A communication system according to claim 1 wherein the saidconnection to the junction of the resistive element and the said diodethereof establishes a reversed potential across the diode.

3. In a communication system according to claim 2, the saidcall-detecting means including relay means connected in common betweenall lines and a second pole of the direct current source in a circuitpath which includes a second uni-directional diode for each lineconnected serially between the relay means and the associated line topermit signalling current of the given direction to flow through therelay means.

4. In a communication system according to claim 3, the said seconddiodes being poled to prevent any reverse current flow therethrough toisolate the relay means from the calling line responsive to the saidpotential reversed connection and to isolate each line from all otherlines.

5. In a communication system, a switchboard terminating a group ofnormally open lines any one of which becomes .closed when calling, adirect-current source comprising a signalling section and a feedingsection connected in series-aiding relationship to provide at leastthree poles comprising a signalling pole, a feeding pole, and at leastone intermediate pole, means grounding one pole other than thesignalling pole, the direct-current source being common to the lines andconnected to each line to supply signalling current flow thereover in agiven direction when calling, the connection of the current source toany line including an individual path comprising a resistive elementadjacent to the signalling pole of the current source in series with auni-directional diode adjacent to the line and including a second pathcomprising a second uni-directional diode adjacent to the line in serieswith call-detecting means which is common to all lines and adjacent toan intermediate pole of the current source, means included in the saidcall-detecting means for detecting signalling current flow over anyline, and connecting means responsive to the detection of signallingcurrent for making a connection to the first path at the junction of thesaid resistive element and the said diode which terminates the said flowof signalling current by masking the potential normally applied throughthe resistive element.

6. In a communication system according to claim 5, the said connectingmeans for masking the potential normally applied through the resistiveelement including means for connecting the grounded one of the saidpoles of the current source of the said junction of the resistiveelement and the associated diode.

7. In a communication system according to claim 5, means including inthe connecting means for connecting the feeding section of thedirect-current source to the calling line to permit feed current flowthereover in a given direction and to restrict such ow through any ofthe associated diodes by applying the potential of the feeding sectionto the answered line with a polarity such that a reversed potential isestablished across the last-said diodes.

8. In a communication system according to claim 7, means included in thecall-answering means for reversing the polarity of the feeding sectionpotential applied to the calling line to reverse the direction of thefeed current ow and to establish a zero potential across the diodes ofthe calling line whereby reversed current How therethrough is prevented.

9. A communication system according to claim 5 wherein any said normallyopen line may be a called line which becomes closed when answered,call-extending means for extending a connection from any calling line toa called line, and means in the call-extending means for applying apotential to the junction of the resistive element and associated diodeof the called line which establishes a reversed potential across thediode when the called line answers to thereby prevent any signalh'ngcurrent ow therethrough.

10. In a communication system according to claim 9, analternating-current ringing source, means for applying the potential ofthe ringing current source to any unanswered called line, and means formaintaining the ringing potential supplied by the said source at adirectcurrent level with'respect to the said potential applied to thesaid junction such that the applied alternating current ringingpotential does not establish a forward potential condition across thediodes associated with the called line during application of ringingcurrent potential thereto.

l1. In a communication system according to claim l0, the means formaintaining the ringing potential at the said level including means forsuperimposing the alternating current ringing potential on adirect-current source having a potential exceeding the potential of anysaid half cycle.

References Cited in the file of this patent UNITED STATES PATENTS

